The present invention relates to hermetically sealed packages for power diodes.
It is the usual practice to market semiconductor power diodes in packages which hermetically isolate the diode from the environment and provide mechanical protection for the diode. Since the price at which such components must be sold depends on the cost of the package and the labor required to fabricate the package, there is a continuing demand for reduction of these costs.
Diode of the type here under consideration, such as planar diodes, mesa diodes, diffused junction diodes, etc., have in common that they have two mutually opposed surfaces constituting, respectively, cathode and anode contact surfaces. Packages for such diodes generally include a base plate, or support member, supporting one diode surface, an insulating frame member made, for example, of ceramic, resting upon the base plate and surrounding the diode, and a cover plate resting upon the frame member and covering the diode. The base plate, the frame member and the cover plate are bonded or cemented together to form a hermetically sealed space enclosing the diode.
Typically, the base plate and the top plate are made of electrically conducting material, one surface of the diode is in electrical contact with the base plate, and the other surface of the diode is connected to the top plate by a connecting element of one type or another.
Connecting elements which have been employed in the prior art include conductive members having a C or S shape and interposed directly between the diode and the top plate. The connection provided by such contact elements has been found to present reliability problems.
Another type of connecting element which has been proposed is constituted by a solid block, or slug, of conductive material interposed between the diode and the top plate. While this eliminates some of the reliability problems posed by older connecting elements, it presents problems associated with creation of the desired hermetic seal in the space containing the diode and mechanical stresses on the diode.
Another connection technique which has been suggested involves the use of a wire bond between the diode and a conductive body connected to the top plate. While this approach solved problems presented by the earlier approaches, the resulting package is costly to manufacture and the wire bonds limited the amount of current which could be carried by the diode.